So far, there is heretofore known a rotation angle detector for detecting such as a shaft that is being rotated or the like (refer to a patent document 1 for example). Regarding such the rotation angle detector, there is formed a magnet therein to be as a disk shape and then to be supported by an axis of rotation therein. Moreover, there is designed such the magnet to be configured as rotatable in a predetermined direction with such the axis of rotation as a center therefor. Further, such the rotation angle detector further comprises magnetic sensors as two units therefor. Still further, such the magnetic sensors as two units are Hall elements, and then there is designed the same to be arranged for having an angle as approximately ninety degrees for between a straight line, that passes through a center of such the disk and through one of the magnetic sensors, and another straight line, that passes through the center of such the disk and through the other one of the magnetic sensors. Furthermore, there is designed each of such the magnetic sensors to be arranged at directly under a circumference of such the magnet respectively.    [Patent Document 1] Japanese Patent Application Publication No. 2003-075108 (claims 2 to 4, FIG. 4 and FIG. 5)